The present invention relates to a speed varying device.
In particular, the present invention relates to speed reducing device, whereto the description that follows shall refer without thereby losing its general nature.
As is well known, speed reducers are mechanical devices provided with an input shaft and an output shaft, which are respectively connected to a motor and to a user unit and are able to drive the user unit itself with a rotatory motion presenting a lesser speed than the speed whereat the aforementioned input shaft rotates.
Such types of reducers substantially comprise a box body for the containment of a plurality of shafts, whereon are splined gears which, in pairs, mutually transmit motion with appropriate transmission ratios and give rise to the aforementioned driving of the output shaft with lesser speed than that of the input shaft. The velocities of rotation of the input and, respectively, of the output shaft, as well as the value of the torque that the output shaft must transmit to the user unit, determine the choice of motor to be associated to each reducer, and oblige to provide the reducer itself with a number of gear pairs equal to or greater than two.
In a first type of known reducer, when there is a need to obtain a total transmission ratio whose value entails the use of a number of gear pairs greater than two, it is necessary to interpose between a casing and a cover, comprised in the aforesaid box body, an additional sector of casing, which supports at least one pair of gears to be added to those already present. Similarly, the cover also needs to be chosen adequately as a function of the transmission ratio to be attained and of the aforementioned torque value, in order to allow coupling to the reducer a motor able to provide at its output a number of rotations per minute and a power suitable for the requirements.
Obviously, the fact of having to construct and hold in stock an appropriate number both of additional covers and of casing sectors, differing from each other, entails a considerable financial burden. In addition, the fact that the aforementioned box body comprises the three aforesaid parts, mutually connected in pairs with interposition of sealing elements, such as respective gaskets for sealing lubricating fluids, entails considerable component complexity for the reducer described above, as well as a greater likelihood of seepage of the lubricant itself.
In a second type of known reducers the casing is constructed in a single body, and it is fitted internally with an additional casing sector which is always present, both in the case of a reducer with two gear pairs, and in the case of a reducer with three or more gear pairs. Such additional casing sector essentially comprises a wall, provided with a number of holes or housings able to receive respective elements for supporting shafts whereon gears are splined. Such housings are in a sufficient number to accommodate the presence of the maximum number of gear pairs with which the reducers in question can be provided. Therefore, even when the reducer is provided with only two gear pairs, the aforesaid casing is fitted with an additional casing sector of considerable constructive complexity, provided with a number of housings exceeding the number actually necessary and characterized by a needlessly high cost of manufacture. Such cost of manufacture is particularly considerable also due to the fact that the mechanical complex constituted by the casing and by the aforementioned additional sector is obtained by casting, using a core of considerable size due to the presence in the complex itself of ample undercuts.
Also known are reducers of the second type described wherein the aforementioned additional casing sector is manufactured separately from the aforesaid casing, and is connected thereto by means of screws or similar connecting means. In this case as well, the manufacturing and/or storage costs of the additional sector, which in case of utilization of two gear pairs is more complex than necessary, are quite burdensome.
It should also be noted that, also in the previously described reducers fitted with an additional casing sector integral with the casing, it is necessary to be able to associate to the reducers themselves motors presenting different characteristics and able to accommodate the various needs. As a consequence of that fact it is necessary, as in the case of the first type of known reducer described above, to produce and stock a plurality of different types of covers suited to meet the various requirements.